In wireless multiple access communications systems, a limited amount of available air link resources, e.g., bandwidth over time, needs to be shared among a plurality of users. A fixed amount of air link resources may be reserved for downlink traffic channel signaling, which is allocated to wireless terminals, e.g., on a per segment basis by a base station scheduler. A base station acting as a point of network attachment for wireless terminals located within its wireless coverage area, e.g., designated sector and/or cell, is limited in the number of active uses which can be serviced to receive downlink traffic channel signals over a given time interval. Such limitations are based on the number and capacity of traffic channel segments available within the given time interval to assign to users. Other factors contributing to user capacity include channel conditions and levels of interference in the system. In some embodiments, for convenience of assignment and to reduce overhead signaling associated with assignment, each of the downlink traffic channel segments include a fixed number of minimum transmission units (MTUs), e.g., the same fixed number of MTUs, that may be used to convey modulation signals. For a given downlink traffic channel segment of fixed size, the number of information bits that can be communicated in a given downlink traffic channel segment is a function of the coding rate selected and the modulation scheme used, e.g., QSPK, QAM16, QAM64 for the segment.
In order to increase the number of active users supported in a sector or cell by a base station point of network attachment, some systems employ superposition signaling, where for a given MTU or set of MTUs, high power signaling is directed to a first user or group of users and low power signaling directed to a second user or group of users, both signals being communicated simultaneously using the same air link resources. The implementation of superposition signaling tends to create interference problems.
Typically, at any given time in a communications system, there is a wide variation of user requests and/or requirements, in terms of downlink traffic channel signaling needs. Some users, e.g., users downloading large data files, video images, programs, etc., may have large amounts of information bits or frames of information bits to receive and would be well served by large size traffic channel segments using block encoding. Other users, e.g., a user receiving a packet of voice information or a short message, may need to receive only a small amount of information bits at one time and would be better served if the downlink traffic channel segment size and coded block size were small. A user may have been receiving a large information bit stream and efficiently utilizing air link resources, but now only requires a small number of addition bits to be communicated to complete the transmission. Typically unused information bit capacity within a coded downlink traffic channel segment may be padded with known values, e.g., zeros, to complete the coding block. However, such implementations waste the air link resource and create unnecessary interference.
Time constraints on the downlink data may also be an important consideration when scheduling users. For example, some users, e.g., in voice applications such as VoIP, may only require small amounts of data to be intermittently transmitted in the downlink; however, the delivery of each small amount of data is timing critical. Some existing downlink traffic channel segment structures, e.g., implementations structured to efficiently communicate data such as, e.g., text or video, may not efficiently facilitate such an embodiment. For example, each downlink traffic channel segment may be structured to include many MTUs to support data applications; however, a typical block of voice information bits to be communicated at one time may be significantly smaller than the number of information bit locations of the downlink traffic channel segment. Timing constraints on the block of voice bits may preclude grouping multiple blocks of voice bits into a single downlink traffic channel segment. Also, the frequent request for downlink traffic channel segments by the voice users may have a tendency to monopolize the available downlink transmission slots and lower the overall system downlink user data throughput.
In addition, at different times, the same wireless terminal may have different downlink data requirements, e.g., as it switches between user applications, digests received data, proceeds to input data to be communicated on the uplink, etc.
In view of the above discussion, it is clear that a need exists for more efficient apparatus and methods to use air link resources for downlink traffic channel signaling in wireless communications systems supporting a plurality of users with a wide range of varying resource needs. Methods and apparatus that allow for both low data rate users and high data rate users to co-exist and share the air link resources, with each employing a coding and modulation technique which efficiently utilizes resources would be beneficial. Techniques which reduce the amount of wasted resource due to unused excessive information bit capacity in segments would also be beneficial. Resource efficient superposition signaling techniques which limit the amount of superimposed signals transmitted within a segment where possible thus limiting interference, yet allowing for the number of active user supported to be increased would also be beneficial.